Thermal energy in interaction with biological matter is being used both in medicine and in the food processing industry. Exchange of thermal energy inside any system or between systems involves heat transfer processes that in turn affect the local temperature and its temporal and spatial distribution. Bioheat transfer analysis in living systems is generally complicated by the fact that the thermal properties are generally nonhomogeneous and anisotropic with considerable variations intra and inter specimen samples. Biological matter responds to the exposure of temperature changes in different ways. Consequently it might be argued that in situ monitoring of the thermal profile inside some confined volume during these procedures is of interest in a variety of applications.
Electromagnetic (EM) fields, from visible and infrared (IR) light to microwave and radio frequency (RF) waves are frequently applied under these circumstances serving as the energy carrier or as the imaging information carrier as is the case in the magnetic resonance (MR) imaging. Strong EM fields disqualify conventional electronic sensors due to absorption of EM energy and induced currents, while fiber optical sensors are dielectric in nature and intrinsically immune to the same fields. It is thus an object to this invention to provide a probe which may be used inside a body being subject to strong EM fields.
Electronic sensors for temperature measurements do not offer immunity versus electromagnetic fields and consequently, precautions have to be taken for effective shielding if they are to be applied under high EM field circumstances.
In Y. Rao, D. J. Webb, D. A. Jackson, L. Zhang, and I. Bennion, “In-Fiber Bragg-Grating Sensor System for Medical Applications”, J. Lightwave Technol., Vol. 15, No. 5, pp. 779–785, 1997 a sensor system is described for use in a human body. No precautions are taken in this case to enable the probe to be used under high EM circumstances. Also, the sensor is not prepared for use at temperatures below −40° C. or above +80° . The tube material, polyamide or nylon, limits the sensor to a temperature range between −40° C. and +80° C. Another disadvantage is that the sensor fiber is in direct physical contact with the environment into which its sheath is inserted through apertures arranged in the wall of the sheath next to each FBG sensor element. Thus biologic solvents will intrude into the lumen of the sheath and possibly influence the stress condition of the fiber. Also, index matching gel is applied at the end of the sensor fiber inside the sheath. The gel will solidify by freezing at low temperatures, causing the fiber to stick to the sheath tubing. Thus this sensor does not comply with precise measurements over a large temperature range.
One particularly important application where temperature monitoring is critical is the expanding field of cryosurgery. Cryosurgery is becoming an important modality for treating a number of varied conditions. One common example is the treatment of prostate cancer by freezing the prostate gland to a sufficiently low temperature to kill the cells within, to ensure that any cancerous cells therein are killed.
To date performing such procedures has been difficult and required great skill on the part of the physician carrying them out. The difficulty is that the physician must ensure that all potentially cancerous cells are killed by being frozen whilst avoiding damage to surrounding tissue and structures such as the rectal wall.
It is therefore a further object of the present invention to provide an improved method of cyrosurgery.
As has been described above, conventional temperature probes cannot be used in conjunction with imaging which utilises high electro-magnetic fields such as Magnetic Resonance Imaging (MRI). This compounds the difficulty in cryosurgical applications of being able to control the freezing process since ultrasound imaging which is used instead can only image the edges of the ice ball formed. The ice ball appears as a uniform dark area on the ultrasound image and thus gives no information on temperature within the ice ball. It has been shown that, under some circumstances, water can be super-cooled to approximately −45° degrees Centrigrade. Thus, the presence of an ice ball is no guarantee that all cells within it boundaries have been killed.
U.S. Pat. No. 5,647,848 to Chinn, the full contents of which are explicitly incorporated herein by reference, describes this problem and seeks to solve it by the use of an increased number of temperature probes. These are, however of the conventional sort and ultrasound imaging must therefore still be used.